Injection devices, such as the Owen Mumford Autopen®, are commonly used by patients to self-administer injections of medicament. Such devices are typically provided in a pen-like body which contains, defines or receives a cartridge or syringe of medicament. The injection device generally comprises a delivery mechanism which is arranged to dispense the medicament via a needle in response to a user pressing a button or trigger.
As many such injection devices are arranged to be either reusable (i.e. the cartridge of medicament can be replaced) or to deliver a plurality of separate injections until the medicament within the device has been fully consumed it is common to arrange the device to receive a disposable, single-use, needle assembly. Such needle assemblies are generally referred to as “pen needles”.
Pen needles comprise a body or hub which is configured to be attached to the injection device in use (for example by means of a screw thread or other removable attachment arrangement) and which supports the needle. Typically, the needle is a double ended needle having a forward end for use in penetrating a user's skin and a rearward end which pierces a septum of a cartridge or syringe in the injection device when the pen needle is attached to the device. It will be appreciated that such syringe/cartridge septa are self-sealing membranes which can maintain the sealing and sterility of the syringe/cartridge over a number of uses. A removable cap may also be provided which initially covers the needle to provide protection against needle stick injuries and to maintain sterility of the needle (and the needle assembly may initially be sealed within the cap by means of removable sterile packaging).
It is known to provide needle assemblies such as pen needles with a shroud which is arranged to cover the needle after use (and in some cases also prior to use) to reduce the risk of accidental needle-stick injuries after use or during disposal of the needle assembly. For example, one form of needle assembly may include a shroud which is arranged to telescope forwardly relative to the hub after use to cover the forward end of the needle. As the needle assembly hub typically has an annular rearwardly extending form (with an internal screw thread interface for attachment to an injection device) and the rearwardly extending portion of the needle is generally of shorter length than the forwardly extending needle portion, the rearward facing end of the needle is partially shrouded by the hub. However, the internal diameter of the rearward portion of the hub is defined by the interface with the injection device and, as such, the applicant has recognised that for at least some devices the resulting opening may be of too large a diameter to prevent the risk of a user's fingertip accidentally coming into contact with the rearward needle tip.
Embodiments of the invention seek to provide improved needle assemblies which may overcome some or all of these problems.